The present invention relates to sodium zirconium carbonate, zirconium phosphate, and zirconium basic carbonate and methods of making these compounds.
Sodium Zirconium Carbonate (SZC) is an amorphorous zirconium polymeric compound with the structural formula as shown: 
The granular form of the material can be obtained by the following two methods:
Method A: Reaction of granular zirconium basic sulfate with a saturated soda ash solution followed by washing the product to remove the sulfate.
Method B: Controlled polymeric particle growth reaction of a metastable sodium zirconium carbonate solution formed by mixing a soluble zirconium salt solution with an excessive amount of soda ash solution.
One industrial application of granular SZC is the conversion of the material to zirconium basic carbonate (ZBC) which is a commercial raw material in making other zirconium chemical products. The conversion can be made by titrating the granular SZC to pH 3.5-4.0 with an acid to remove the excessive sodium carbonate. The granular SZC used for making ZBC is usually produced by Method A. Another important application of SZC is the conversion of the material to the granular zirconium chemical ion exchangers, namely, zirconium phosphate (ZrP) and hydrous zirconium oxide (HZO). These zirconium ion exchange material are used commercially for renal dialysis application. The quality and economic criteria, which dictate the method of their manufacture, constitute the art of making the REDY(copyright) sorbent cartridge for hemodialysate regeneration currently used by SORB(trademark) Technology, Inc., Oklahoma City, Okla. A recent study on the design of a sorbent cartridge at SORB(trademark) Technology, Inc. for peritoneal dialysis (PD) fluid regeneration indicates that the granular SZC by itself has unique properties which make it more beneficial than HZO in contributing to the potency of the sorbent PD cartridge. These properties of the material which make the cartridge adaptable to the PD treatment conditions may be summarized as follows:
1. The material has sufficient phosphate adsorption capacity to remove phosphate from the patient fluid for the treatment of hyperphosphatemia in renal disease patients.
2. The material supplements bicarbonate to the PD fluid, which can be essential to correct metabolic acidosis in patients.
3. The material prevents the pH of PD fluid from falling, which may cause depletion of bicarbonate from the patient. This allows regenerative PD to be feasible.
In order to manufacture the granular SZC for sorbent PD applications, both quality and economic factors have to be considered. Method A cannot be used because the product has high sulfate content that degrades the quality of the material as a sorbent. Method B has been used in production through the use of acid zirconium sulfate tetrahydrate (AZST) as the zirconium raw material. The process efficiency is less and the manufacture cost is higher for this process, but the ZrP made from granular SZC has higher ammonium adsorption capacity than that made from zirconium basic sulfate (ZBS).
While these processes are useful, there is a need to provide a better quality sodium zirconium carbonate and zirconium basic carbonate with uses especially in the dialysis area and further there is a need to reduce the cost of manufacturing these components.
The feature of the present invention is to provide an improved sodium zirconium carbonate.
A further feature of the present invention is to provide improved methods to make the sodium zirconium carbonate.
An additional feature of the present invention is to provide a method to make zirconium basic carbonate.
Also, a feature of the present invention is to provide methods to make the zirconium basic carbonate.
Another feature of the present invention is to provide an improved zirconium phosphate and methods to make zirconium phosphates.
An additional feature of the present invention is to provide methods to make the sodium zirconium carbonate, zirconium phosphate, and zirconium basic carbonate more economically and to provide methods which result in a better quality product.
Additional features and advantages of the present invention will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention. The objectives and other advantages of the present invention will be realized and obtained by means of the elements and combinations particularly pointed out in the written description and appended claims.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, the present invention relates to a method of making sodium zirconium carbonate which involves heating zirconium oxychloride with soda ash at a sufficient temperature and for a sufficient time to form the sodium zirconium carbonate. Preferably, the soda ash is in the form of an aqueous slurry or solution and the zirconium oxychloride is in the form of a powder or solution. Prior to the heating, the zirconium oxychloride and soda ash are preferably agitated or mixed by other means to form a solution mixture at ambient temperatures, such as room temperature. After the heating step, the sodium zirconium carbonate can be washed to remove impurities and any chloride.
The sodium zirconium carbonate, after the initial preparation can be subjected to a titration. Preferably, an alkaline slurry contains the sodium zirconium carbonate and the titration occurs with at least one acidic agent, such as an acid, to obtain a pH below about 7.0. Other additional steps can be used in this process, such as filtering steps, washing steps, and drying steps.
The present invention further relates to a sodium zirconium carbonate which contains from about 2 weight percent to about 5 weight percent Na+;
from about 44 weight percent to about 50 weight percent ZrO2;
from about 12 weight percent to about 18 weight percent CO32xe2x88x92; and
from about 32 weight percent to about 35 weight percent H2O, based on the weight of the sodium zirconium carbonate.
The present invention, in addition, relates to a method of making zirconium basic carbonate which involves titrating an aqueous slurry of a sodium zirconium carbonate to a pH of from about 3.5 to about 4 with an acidic agent. The sodium zirconium carbonate used to form the slurry has a preferred moisture content of from about 15% to about 25% LOD. After titrating, the aqueous slurry is washed with water. The zirconium basic carbonate can then be recovered as a wet powder from the slurry by various techniques.
In addition, the present invention relates to a zirconium basic carbonate characterized by a Na+ content of less than about 1000 ppm;
a ZrO2 wt % of from about 35 wt % to about 40 wt %; and
a CO32xe2x88x92 of from about 8 wt % to about 10 wt % wherein the weight % is based on the composition of the solid powder (final product). Unless stated otherwise, all % and wt %, throughout this application, are wt % based on the weight of the final product.
The present invention further relates to a method of making zirconium phosphate which involves heating zirconium oxychloride with soda ash at a sufficient temperature and for a sufficient time to form sodium zirconium carbonate and treating the sodium zirconium carbonate with caustic soda to form an alkaline hydrous zirconium oxide. Afterwards, the alkaline hydrous zirconium oxide is heated as a slurry, and an acidic agent(s) such as phosphoric acid, is added. After heating, the slurry can be cooled and an acid zirconium phosphate can be filtered off and washed to reduce unreacted leachable phosphate levels. An aqueous slurry can then be formed with the acid zirconium phosphate and this slurry can be titrated with a basic agent, such as caustic soda, until a desired pH is reached, such as a pH of from about 5 to about 6. Afterwards, the titrated product, which is titrated zirconium phosphate, can be filtered and washed to preferably reduce the leachable sodium ions. Then, the zirconium phosphate can be dried to form a free flowing powder preferably having a moisture level of from about 12 to about 18% LOD.
The present invention further relates to a novel zirconium phosphate which preferably has a Na+ content of from about 4 to about 6 wt %; a ZrO2 wt % of from about 34 wt % to about 37 wt %; a PO4xe2x88x92% of from about 41 wt % to about 43 wt %; and a H2O wt % of from about 14 wt % to about 18 wt %, based on the weight of the zirconium phosphate. The zirconium phosphate of the present invention preferably has a good adsorption capacity for ammonia, Ca2+, Mg2+, and toxic heavy metals. Preferably, the zirconium phosphate has no residual sulfate or chloride and satisfies other characteristics desirable in dialysis applications or other ion exchange applications.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide a further explanation of the present invention, as claimed.